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Stress simulation in the ILC positron target with ANSYS

Stress simulation in the ILC positron target with ANSYS. Felix Dietrich (TH-Wildau), Sabine Riemann, Friedrich Staufenbiel (DESY). Outline. Alternative source Goal of the studies Model Implementation into ANSYS Temperature calculation Results Summary Next steps. Alternative source.

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Stress simulation in the ILC positron target with ANSYS

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  1. Stress simulation in the ILC positron target with ANSYS Felix Dietrich (TH-Wildau), Sabine Riemann, Friedrich Staufenbiel (DESY)

  2. Outline • Alternative source • Goal of the studies • Model • Implementation into ANSYS • Temperature calculation • Results • Summary • Next steps

  3. Alternative source • Suggested by T. Omori et al., see also NIMA672 (2012) 52 • Uses beam (“conventional” source) of 6GeV • Target: Tungsten • 300Hz scheme • Stretch ILC bunch train (~1ms) to 63ms  lower peak heat load • Stacking of in the damping ring • ILC time structure achieved by extraction scheme from damping ring • Benchmark from SLC target: Peak Energy Deposition Density (PEDD) should not exceed 29J/g • Electron beam parameters are selected accordingly

  4. Goal of the studies • Beam parameters are given ( ~29J/g peak energy deposition @SLC) • How is the dynamic stress evolving in the target with 300Hz scheme in the tungsten target • Target lifetime depend on static and dynamic stress • Energy deposition within fraction of a nanosecond  instantaneous temperature rise • Reaction of material within milliseconds  Stress dynamics • Benchmark: SLC target • But SLC number of positrons per second was about 50 times lower than at ILC

  5. Model • Model 1– Modified SLC target • Fe – ring & Ag – coat & W – core • Radius for beam line @ target = 10.75cm • Model 2– cylinder with diameter correspondingto beam spot size • W – Layer & Ag – Layer • Beam spot radius =0.8cm • Radius of the whole model is r=2.2cm • Parameters for both models • Particle shower has been calculated with FLUKA • Average energy deposition in the target: • 35kW without silver layer • 49kW with silver layer

  6. Implementation into ANSYS • Mesh • Mesh size is related to time steps •  is given  = velocity of sound =5180 m/s • Model 1 : 22124 elements • Model 2 : 9419 elements • Elements: Hexagonal elements • Time structure • 1stattempt: Every bunch is calculated. the length of one bunch is 250ps • 2nd attempt: Linear rise of the temperature in one mini train • Calculation & Results • Model 1: first Calculations could be done. But there is still some work to do. • Model 2: works well, needs less computing time

  7. Temperature calculation • With good mesh, the temperature change resulting from energy deposition by each bunch shows regular behavior with negligible numerical errors

  8. Temperaturerise: 1st attempt • The temperatureincreases per bunchby 1.6K • The graphshowsthetemperatureriseforthefirsttriplet

  9. Results: Stress evolution – Model 2 • The Picture shows the equivalent stress (von-Mises) at diferent positions in the Material • The Picture was taken at: 1.0205 µs • (t=5ns first bunch of mini train) • Deformation is scaled by 730 for visualization; max. surface displacement is about 8µm

  10. Result: Short time – Model 2 • Resultsarecalculatedfor 1µs • Redlineshows max. stress at anygivenpoint at one time • The otherlinesarecalculated an thecenterofthedisc at different depth (1.4cm equalsthesurface; 0.9cm equals a depthof 0.5cm)

  11. Result: Conclusionshort time • Max. temperature rise by one triplet is T=210°C within ~1ms • Heat dispersion into the target body within microseconds is negligible  temperature of the target body is 22°C • Max. stress after one triplet 377MPa • Every mini train adds a different stress load • First mini train +225MPa • Second mini train +110MPa • Third mini train +37MPa • Max. stress by one triplet is below fatigue stress limit 377MPa<520MPa

  12. Results: Long time • First attempt  2 µs pause • Same configuration like the first graph • Results arepreliminary

  13. Temperaturerise: 2nd attempt • The temperatureriseslinearlyoverthewhole mini train • Thatsavescomputing time

  14. Resultsfor 2nd attemept: Model 1 • Resultsarecalculatedfor 3µs • Max. stress isabout 400MPa • Results are preliminary

  15. Resultsfor2nd attempt: Model 2 • Resultsarecalculatedfor 3µs • Max. sressisabout 420MPa • Results arepreliminary

  16. Summary • Maximum dynamic stress per triplet is about 377MPa (fatigue stress limit is 520MPa) • longer time  Stress rise up to 425MPa for both attempts • Load cycles per year at one spot : cycles • With target rotation the number of load cycles at the same beam spot volume can be kept below

  17. Next steps • Simulations of a longer period: • Few triplets • Include target rotation • Check whether interferences of stress waves are possible • Degradation of material is expected due to irradiation • evaluation of dynamic load has to be repeated with modified parameters

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